Along with miniaturization and higher integration of semiconductor integrated circuits, a semiconductor exposure apparatus (hereinafter referred to as “exposure apparatus”) has been required to have higher resolving power. For this reason, shortening of the wavelength of light that is emitted from an exposure light source is under development. As an exposure light source, a gas laser apparatus is used instead of a conventional mercury lamp. Currently, as a gas laser apparatus for exposure, a KrF excimer laser apparatus configured to emit ultraviolet light with a wavelength of 248 nm or an ArF excimer laser apparatus configured to emit ultraviolet light with a wavelength of 193 nm is used.
As current exposure technology, immersion exposure has been put to practical use. In the immersion exposure, a gap between an exposure lens in an exposure apparatus and a wafer is filled with fluid, thereby an apparent wavelength of the exposure light source is shortened by changing the refractive index. In a case where immersion exposure is performed using an ArF excimer laser apparatus as an exposure light source, a wafer is irradiated with ultraviolet light whose wavelength in water is equivalent to 134 nm. This technique is referred to as “ArF immersion exposure (or ArF immersion lithography)”.
Natural oscillation amplitudes of KrF and ArF excimer laser apparatuses are as wide as approximately 350 to 400 pm. Therefore, use of the exposure lens causes chromatic aberration, thus lowering the resolving power. Therefore, a spectrum line width (spectrum width) of a laser beam that is emitted from a gas laser apparatus needs to be narrowed to such an extent that chromatic aberration can be ignored. For this reason, narrowing of a spectrum width is achieved by providing, in a laser resonator of a gas laser apparatus, a line narrow module having a line narrow element (an etalon, a grating, or the like). A laser apparatus whose spectrum width is narrowed in this way is referred to as “line narrowed laser apparatus”.
As means for fine pattern exposure using a KrF or ArF excimer laser apparatus, an exposure apparatus configured to perform exposure using the Talbot effect has been proposed.